1. Field of the Invention
The present invention generally relates to communication systems, and more specifically to techniques for establishing communication between entities in a communication system.
2. Background
The present invention addresses issues relating to communication systems, and specifically point-to-multipoint communication systems. In conventional point-to-multipoint communication systems, a network supports bidirectional data communication between a central entity and multiple customer premise equipment (CPE). Example point-to-multipoint communication systems include cable modem systems, fixed wireless systems, and satellite communication systems. In each system, the communication path from the central entity to the CPE is typically referred to as the downstream, while the communication path from the CPE to the central entity is typically referred to as the upstream.
One type of point-to-multipoint system is a cable modem system, which typically includes a headend that is capable of communicating with multiple CPE, each of which provides cable modem functionality. In a cable modem system, the CPE can be a cable modem, a settop box, or a cable gateway, to provide some examples.
DOCSIS (Data Over Cable Service Interface Specification) refers to a group of specifications published by CableLabs® that define industry standards for cable headend and cable modem equipment. In part, DOCSIS sets forth requirements and objectives for various aspects of cable modem systems including operations support systems, management, data interfaces, as well as network layer, data link layer, and physical layer transport for data over cable systems. The current version of the DOCSIS specification is version 2.0, and includes the DOCSIS Radio Frequency Interface (RFI) Specification SP-RFIv2.0-I03-021218 (hereinafter “DOCSIS RFI Specification”), the entirety of which is incorporated by reference herein.
Conventional DOCSIS-compliant systems use a specific process for CPE joining the network for the first time. In this process, a CPE scans downstream channels, selects a usable downstream channel with an associated usable upstream channel, and attempts to range on the upstream channel using contention slots. Ranging is a DOCSIS-defined protocol by which a CPE establishes communication with the CMTS. A contention slot is a time period during which a CPE is permitted to attempt ranging on a particular channel. Many CPE of the system often contend for the same channel and the same contention slots.
If a CPE loses power after it has successfully joined a network, when power is restored the CPE attempts to re-establish communication with the CMTS in a process that is sometimes referred to as a “cold boot.” After power is restored, the CPE initially attempts to range on the upstream and downstream channels the CPE was previously using. Typically, upstream and downstream channels are shared by many CPE. During power outage situations in which many CPE are impacted, the ranging process can take a very long time due to multiple CPE attempting to range on the same upstream and downstream channels. With the expansion of DOCSIS support into various types of CPE, this problem can result in very long time periods for reacquisition.
What is needed, then, is a method and apparatus for establishing communication between entities in a communication system that addresses one or more of the aforementioned shortcomings of conventional communication systems and methods.